The present invention relates to polymerization catalyst compounds, catalyst systems including these catalyst compounds, and to their use in the polymerization of ethylene and at least one comonomer. In particular, the invention relates to a catalyst system comprising a poor comonomer incorporating catalyst compound and a good comonomer incorporating catalyst compound. Preferably, the low comonomer incorporating catalyst compound is a metallocene containing at least one substituted or unsubstituted fused ring cyclopentadienyl based ligand which is substantially directed to the front of the molecule, contains a long bridging group, or contains a 1-substituted bisindenyl ligand which has been determined to correlate to poor comonomer incorporation. The invention also relates to methods of selecting the poor comonomer incorporating metallocene to pair with the good comonomer incorporating metallocene, to polymers prepared utilizing the catalyst systems of the invention, and to articles, especially polyethylene based film, having enhanced properties produced therefrom.
Metallocene catalyst compounds that incorporate comonomer poorly, typically show very low activity. In addition, polymer molecules having low comonomer content are generally more crystalline and have a high melting temperature, which is disadvantageous in applications such as film where softness or clarity is desired. However, polymers produced by these low incorporators have been shown to be useful in preparing polymer blends. Such blends, for example, include two polymers with each polymer having the same molecular weight, but different comonomer content. Typically these blends have improved mechanical, physical and/or chemical properties and produce articles of manufacture with superior properties. For example, polymer blends prepared with broad bimodal composition distributions consisting of two narrow populations are known to have superior properties such as high tear values in films.
U.S. Pat. No. 5,382,630 to Stehling et al. discloses linear ethylene interpolymer blends made from components that can have the same molecular weight but different comonomer contents, or the same comonomer contents but different molecular weights, or comonomer contents that increase with molecular weight.
U.S. Pat. No. 6,051,728 to Resconi et al. discloses a class of metallocene compounds having two substituted cyclopentadienyl rings bridged by an alkylidene group wherein the groups can be indenyl groups. The metallocenes are characterized by (i) the cyclopentadienyl groups are substituted at the 3-position with a substituent other than hydrogen while the 2-position bears a hydrogen or is part of a condensed benzene ring; (ii) the bridge is a substituted-methylene bridge; and (iii) the cyclopentadienyl groups are identically substituted. These catalyst compositions are utilized in olefin polymerization and particularly in propylene polymerization. However, catalysts with short bridges, such as methylene bridges, particularly those with indenyl or flourenyl ligands, are generally known to have very high comonomer incorporation.
Angew. Chem. 101 (1989) No. 11, 1536 Herrman, Rohrmann et al. discusses four atom bridged bis-indenyl metallocenes.
There is a need in the industry for the ability to identify polymerization catalyst compounds having low comonomer incorporation and enhanced activity to produce polymers and polymer blends with enhanced properties.
In addition, there is a need in the industry for catalyst systems to produce polymers with enhanced properties imparted by catalyst systems including poor comonomer incorporating catalysts to produce polymers, utilizing more than one catalyst in a single reactor.
The present invention is directed to polymerization catalyst systems which include a good comonomer incorporating catalyst compound and a poor comonomer incorporating metallocene catalyst compound, which contains at least one fused ring cyclopentadienyl based ligand, and to the catalyst systems use in olefin(s) polymerization processes. The poor comonomer incorporating metallocene compound contains one or more fused ring cyclopentadienyl based ligand which may be hydrogenated or substituted, and which may be bridged or unbridged to another ligand.
The invention is also directed to the selection of poor comonomer incorporating catalyst compounds to pair with good comonomer incorporating catalyst compounds to form catalyst systems for olefin(s) polymerization to produce polymers having enhanced properties that are easy to process, and especially to produce polymer films having enhanced properties. The preferred polymerization processes are gas phase or slurry phase processes, and are most preferably gas phase processes, especially where the catalyst system is supported.
In one embodiment, the invention provides for a polymerization process for the polymerizing of ethylene in combination with one or more other olefin(s) comonomers in the presence of a catalyst system comprising a poor comonomer incorporating metallocene catalyst compound and a good comonomer incorporating catalyst compound.
In another embodiment, the catalyst system of the invention including a poor comonomer incorporator and at least one second catalyst compound is utilized to prepare polymers in a single gas phase reactor.
In another embodiment the catalyst system of the invention includes substantially the rac isomer, both the rac and meso isomers, or substantially the meso isomer of the metallocene catalyst compounds, preferably of the poor comonomer incorporating metallocene catalyst compound.